The objectives of the proposed research are to evaluate alterations in intrarenal metabolism of sodium in hypertension and chronic retention. The evaluation will be in terms of: 1) identification of the nephron sites of altered sodium reabsorption using micropuncture techniques and 2) tests of hypothesis of mechanisms for regulation of sodium reabsorption including the role of glomerular filtration rate, hydrostatic and colloid oncotic pressures in the peritubule microcirculation and hormones including mineralocorticoids and a proposed natriuretic hormone. These problems will be studied utilizing micropuncture techniques in dogs, rats and hamsters.